Subject matter of the invention is a method and device for obtaining and detecting immunologically active substances (e.g. drugs of abuse) from the gas phase by means of an immunological procedure.
The detection of immunologically active substances from the gas phase has gained particular importance for the detection of drugs of abuse, such as cocaine and cannabinoids.
To date, various techniques and technologies (X-ray instruments, GC-MS coupling, GC with chemiluminescence detectors) are used to carry out stationary tests for the presence of illegal drugs of abuse, e.g. in baggage. However, size and weight of these systems and the high costs involved contradict the common use of these techniques. Principally, all portable instruments whose function is based on ion mobility spectroscopy (IMS) are suitable for use anywhere. They involve, however, problems with respect to selectivity and sensitivity. Moreover, these instruments are only suitable to detect contamination which is present in the form of particles. The only method for the selective detection of narcotics in the gas phase is currently the use of drug-sniffing dogs. The disadvantage involved with the use of such animals is, however, the short time for which the animals are available, the fact that they can be distracted, the presence of irritating substances, and the high costs. A portable instrument for the selective detection of narcotics which can be used under various conditions would, hence, constitute an enormous progress in the fight against illegal drug trafficking.
Biosensors making use of the principle of an immunological reaction between the analyte and binding partners contained in the biosensor would be potentially suitable for such tasks due to the high selectivity and specificity of the immunological reactions. A biosensor of this kind has been described by Ngen-Ngwainbi, J., et al. in J. Am. Chem. Soc. 108 (1986), 5444-5447. In this literature reference, an antibody to a cocaine metabolite (benzoylecgonine) as a reactive component of the sensor is used as a Piezo transducer with a resonance frequency of 9 MHz. The antibody is immobilized through physical adsorption on the surface of the sensor. The lower detection limit is at 0.5 ppb corresponding to 2xc3x9710xe2x88x9211 mol/l in gas phase (for cocaine and cocaine-HCl). As the mass sensitivity of the transducer is very low, the performance of such an instrument is not suitable for use in the practice.
Another method is described in JP-A-0374460. In this literature reference, drug molecules from the gas phase are adsorbed to a polyethersulfone membrane, then eluated and detected in the eluate in an immunological reaction. Again, the sensitivity is very low.
Another method is described in DE-A 41 21 493. According to this reference, immobilized antibodies and labeled tracers (which correspond to the analyte) are bound to one another and present in a permeable, non-transparent partial area of the carrier. The analyte is added and replaces labeled tracers prior to binding to the antibody. The free labeled tracer diffuses then into a transparent part of the carrier. The progress of the tracer diffusion can be monitored as it causes a discoloration, since the label used in the tracer is a dye. Again, this is a method which exhibits a very low sensitivity.
The detection limits necessary for a successful detection of drugs of abuse from the gas phase cannot be reached with these methods.
Cocaine, for example, has a saturation concentration of 6xc3x9710xe2x88x9212 mol/l gas phase at 20xc2x0 C. In the practice, however, concentrations are considerably lower so that the lower detection limit of a method necessary for successful detection ranges between 10xe2x88x9213 to 10xe2x88x9215 mol/l gas phase.
As it is not possible to measure such low concentrations directly from the gas phase, a device for determining immunologically active substances from the gas phase advantageously comprises an adsorption unit and a detection unit.
In the fight against drugs, it is also necessary to detect particle-like drugs or drugs that are bound to particles in addition to drug molecules which occur freely in the gas phase (edited by BKA, xe2x80x9cInternationales Symposium Detektion von Rauschgiftxe2x80x9d, Wiesbaden 1991).
It is an object of the present invention to provide a method of obtaining immunologically active substances from the gas phase which can be used to convert the substance to be detected from the gas phase into a form suitable for subsequent detection reactions.
Another object of the invention is the provisision of a method of determining immunologically active substances from the gas phase which exhibits a high sensitivity and allows quick adsorption or adsorption and determination.
Immunologically active substances from the gas phase are substances which occur freely in the gas phase, particles of these substances or substances bound to particles which can be obtained from the gas phase.